Can testing



Dec. 17, 1968 G. B. LINDERMAN ETAL CAN TESTING 2 Sheets-Sheet 1 Filed March 51, 1967 FIGJ INVENTORS a N H VA 6 M R R 0. E 0 T m S A B G TT E M w 1968 G. B. LINDERMAN ETAL 3,416,559

CAN TESTING FIG.2

INVENTORS GARRETT B. LINDERMAN a HARRY T. GIBSON ATTORNEY United States Patent 3,416,659 CAN TESTING Garrett B. Linderman, Washington, D.C., and Harry T.

Gibson, Gaithersburg, Md. (both Linderman Engineering Co., Inc., 8814 Brookville Road, Silver Spring,

Filed Mar. 31, 1967, Ser. No. 627,454 Claims. (Cl. 209--111.7)

ABSTRACT OF THE DISCLOSURE A casing traversed by an endless belt containing openings with which cans to be tested are registered and suitable hold-down means is provided to maintain the cans in light-tight relationship with the belt sothat when light is directed upon the external surfaces of the cans, due to the reflective properties of the can surfaces, and the spacing between adjacent cans, light will be imposed upon the entire outer surfaces of the cans so that it will pass through the can wall should there be a pin hole present, to energize a photosensitive device disposed on the opposite side of the belt from the cans themselves. By means of a pulse generator driven in synchronism with the belt and signals from the photosensitive device or devices, a shift register is actuated so that any can containing a pin hole will be rejected at a point downstream from the inspection station.

Specification This invention relates to can testing and is particularly adapted for the testing of cans having reflective internal and external surfaces. It is eminently suited for deep drawn seamless aluminum cans, but is applicable to a variety of types of cans.

There has been great difliculty in the past in the detection of pin holes occurring in the walls of cans, since the application of light to the entire surfaces of such cans has posed a real problem.

The inspection apparatus for cans having reflecting internal walls and open at one end contemplated by the present invention comprises an endless opaque conveyor belt containing openings for registration with and of less diameter than the open ends of the cans to be inspected, means for driving the belt, a source of light adjacent the belt for illuminating external surfaces of the cans and penetrating any opening in such surfaces, photosensitive means adjacent the belt for sensing any light from the source penetrating the surface and passing through the open ends and belt openings, means for producing lighttight engagement between the cans and belt, means shielding the photosensitive means against ambient light and against direct light from the source, and means responsive to the photosensitive means for discriminating between light-tight cans and cans whose surfaces are penetrated by light from the source.

The means for producing the light-tight engagement between the cans and belt may include a source of subatmosphericpressure, but other hold-down means are contemplated. A voltage source is provided for energizing the light source together with means for modulating the light at a frequency Well above 120 cycles per second so as to distinguish the activating light from ambient light, and the light source preferably produces predominantly ultraviolet light and illuminates the entire external surfaces of the cans. A housing encloses the photosensitive means, and has an open end adjacent the belt, and a vacuum pump connected to the interior of the housing may be used to provide a subatmospheric pressure in the housing and in the cans to cause the cans to engage the belt in light-tight relationship. The casing preferably provides a support for the belt so that it will not sag in the areas engaged by the cans undergoing test. The photosensitive means is arranged in circuit with a memory system for rejecting defective cans at a station beyond the photosensitive means. The openings are mutually spaced so that cans in registry therewith will be spaced by a distance of from two-tenths to eighttenths of the diameters of the cans undergoing inspection. The casing provides reflective surfaces adjacent the light source for directing light from the source towards the cans undergoing inspection.

A more complete understanding of the invention will follow from a description of the accompanying drawings wherein:

FIG. 1 is a perspective view, partially broken away, illustrating the present invention;

FIG. 2 is a side elevation, partially broken away depicting the apparatus of FIG. 1 in conjunction with electric circuits in block diagram form constituting part of the invention; and

FIG. 3 is a sectional elevation taken along line 3-3 of FIG. 2.

A casing 10 closed on all surfaces except its upper surface, carries on its supper surface a belt guide 12 providing slots 14 so that the edges of the belt will be shielded by the projecting portions 16 of the guide to exclude ambient light. The guide is provided with small openings 18 for communication with the interior of the casing and larger openings 20 through which light penetrating openings in the walls of the cans undergoing inspection so that such light can be sensed by photosensitive devices, such as photomultiplier tubes 22. The smaller openings 18 are provided with nipples 24 projecting into the casing 10. Within the casing 10 there is provided a housing 26 surrounding the photosensitive devices 22. The casing is provided with a suitable fitting 28 to which is coupled a pipeline 30 extending to a vacuum pump. The casing is provided with partitions 34 for re inforcing purposes, but these partitions contain openings 36 so that the entire casing can be evacuated.

Supported above the casing, there is a hood 36 whose internal surface is reflective so that light produced by the sources 38 will be confined within the hood and directed towards cans 40 undergoing inspection.

A belt 42 is driven by a pulley 44 and supported by lower idler pulleys 46 and an upper idler pulley 48. The driving pulley 44 is driven by a motor 50 connected thereto by means of a shaft 52.

Openings 54 formed in the belt are intended for registry with the cans undergoing inspection, and these openings are somewhat smaller than the openings in the open ends of the cans so that when suitable hold-down means are applied, there will be a fluid-tight seal between the cans and the belt so that there will be no leakage of am bient light to actuate the photosensitive devices.

The light sources are supplied from a voltage source 56 in circuit with a modulator 58 providing a frequency well above cycles per second permitting the use of band-pass filters so that the response of the light responsive means will discriminate between ambient light and modulated light to avoid any false signals.

The output from the photomultiplier tubes 22 is applied through leads 60 to a band-pass filter having a bandpass frequency corresponding to the modulated frequency of the light source, whose output supplies an amplifier 62 which feeds a detector 64 whose output is fed to a Schmitt trigger 66 whose output is in turn applied to a shift register 68, which is also fed from a pulse generator 70 connected with the driving pulley 44 to provide a memory system for actuating a reject solenoid 72 and a reject gate 74 located at a station beyond the light sensing station so as to reject any can that may contain a pin hole.

By virtue of the fact that the cans for which the present invention is primarily intended have reflective surfaces internally and externally, it will follow that the external walls of each can will serve as reflectors for directing light to all portions of adjacent cans, and the internal surfaces will cause light to be reflected and re-reflected where it penetrates the wall of any can so that the light will impinge upon one or more photosensitive devices to indicate the occurrence of a pin hole.

Where a vacuum pump is used to produce the holddown effect, as indicated in the drawings, upon the application of a vacuum to the interior of the casing, cans in registry with the openings 54 will be drawn into tight engagement with the belt so as to preclude the leakage of light.

The spacing of the openings 54 is important since it has been found that where the cans are spaced from one another by a distance of from two-tenths to eight-tenths of the can diameter, the impingement of light on the entire external surfaces of the cans will be optimum, thereby reducing the chances of missing a pin hole.

Whereas only one form of the invention has been depicted in the accompanying drawings, variations within the scope of the appended claims will suggest themselves to those skilled in the art.

We claim:

1. Inspection apparatus for cans having reflecting internal walls and open at one end, comprising a casing, an endless opaque conveyor belt containing openings for registration with and of less diameter than the open ends of cans to be inspected, means for driving said belt, a source of light adjacent said belt for illuminating external surfaces of said cans and penetrating any opening in said surfaces, photosensitive means adjacent said belt for sensing any light from said source penetrating said surface and passing through said open ends and belt openings, means for producing light-tight engagement between said cans and belt, means shielding said photosensitive means against ambient light and against direct light from said source, and means responsive to said photosensitive means for discriminating between light-tight cans and cans whose surfaces are penetrated by light from said source.

2. Inspection apparatus according to claim 1 wherein said means for producing light-tight engagement between said cans and belt includes a source of subatmospheric pressure.

3. Inspection apparatus according to claim 1 including a voltage source for energizing said light source, means for modulating light produced by said light source, and band-pass filter means having a band-pass frequency corresponding to the modulated frequency of the light source in an output circuit supplied by said photosensitive means.

4. Inspection apparatus according to claim 1 wherein said light source produces predominantly ultraviolet light.

5. Inspection apparatus according to claim 1 wherein said light source illuminates the entire external surfaces of said cans.

6. Inspection apparatus according to claim 1 wherein a housing encloses said photosensitive means, said housing having an open end adjacent said belt, and a vacuum pump connected to the interior of said housing provides a subatmospheric pressure in said housing and in said cans causing said cans to engage said belt in light-tight relationship.

7. Inspection apparatus according. to claim 1 wherein said casing provides a support for said belt.

8. Inspection apparatus according to claim 1 wherein said photosensitive means is in circuit with a memory system for rejecting defective cans at a station beyond said photosensitive means.

9. Inspection apparatus according to claim 1 wherein said openings are mutually spaced so that cans in registry therewith will be spaced by a distance of from two-tenths to eight-tenths of the diameters of the cans undergoing inspection.

10. Inspection apparatus according to claim 1 wherein said casing provides reflective surfaces adjacent said light source for directing light from said source towards said cans.

References Cited UNITED STATES PATENTS 3,133,640 5/1964 Calhoun 209-111.7 3,292,785 12/1966 Calhoun 250-223 M. HENSON WOOD, JR., Primary Examiner.

R. A. SCHACHER, Assistant Examiner.

US. Cl. X.R. 250--223 

